Radio wave lens antenna

ABSTRACT

A multi-beam lens antenna for individual communication with communication satellites spaced at small elongations. The multi-beam antenna comprises primary feeds  3  each of which is composed of a waveguide having an opening at the end and a dielectric body  6  disposed at the end, a hemispherical Luneberg radio wave lens, and a reflective plate attached to the circular opening of the hemispherical radio wave lens and adapted for reflecting a radio wave incoming from the sky or emitted toward a target. The waveguides are preferably rectangular waveguides  4  rather than circular waveguides  5 . The dielectric bodies  6  are preferably tapered.

RELATED APPLICATION

This application is the U.S. National Phase under 35 U.S.C. § 371 ofInternational Application No. PCT/JP2004/007613, filed on Jun. 2, 2004,which in turn claims the benefit of Japanese Application No.2003-161128, filed on Jun. 5, 2003, and Japanese Application No.2004-156002, filed on May 26, 2004, the disclosures of whichApplications are incorporated by reference herein.

1. Field of the Invention

The present invention relates to a radio wave lens antenna for wirelesscommunications, which is constructed by combining a spherical orhemispherical Luneberg radio wave lens for focusing radio wave beam withcompact primary feeds.

2. Background of the Invention

FIG. 1 schematically shows an antenna using a hemispherical Lunebergradio wave lens. In FIG. 1, reference numeral 1 denotes a hemisphericalLuneberg radio wave lens (hereinafter, referred to as ‘radio wave lens’)for focusing radio wave beam. Reference numeral 2 indicates a reflectiveplate attached to the half-cut flat surface of the sphere of the radiowave lens 1 to reflect a radio wave incoming from the sky or radiatedtoward a target, while reference numerical 3 designates a primary feedfor transmitting and receiving a radio wave. The primary feed 3 issupported by an arch-type arm or the like (not shown) and is configuredto be positioned at an arbitrary radio wave focus point of the radiowave lens 1.

In case of receiving a radio wave in this radio wave lens antenna, forexample, a radio wave A incoming from a certain direction reaches thereflective plate 2, after the propagation direction thereof is bent bythe radio wave lens 1, and then is reflected by the reflective plate 2to be focused at an opposite side of the lens with respect to the centerof the lens as shown in FIG. 1. Thus, the focused wave can be receivedby the primary feed 3. This means that radio waves from randomdirections above the reflective plate 2 can be received; in other words,an arbitrary point of the hemisphere of the radio wave lens 1 can be afocal point.

On the other hand, in case of transmission, a reversibility of theprocess described above can be applied.

Further, although the focal point is shown to be on the surface of thelens in FIG. 1, in reality, the focal point is normally formed aslightly outside the lens surface (generally varied in the range from 0mm to 100 mm).

Considering the above characteristics, radio waves can be independentlyreceived or transmitted from or to a plurality of (N) geostationarysatellites which reside in a plane including the equator, by preparing aplurality of (N) primary feeds 3 and installing some at focal points ofthe respective geostationary satellites. It is a great advantage of thepresent radio wave lens antenna that one radio wave lens can communicatewith N satellites.

However, in order to use the radio wave lens antenna as a practicalmulti-beam lens antenna, the problems described below should be solved.

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

For example, in Japan, since communication satellites are locatedadjacent to each other at every 4 degrees interval (2 degrees in foreigncountries), the elongation between those communication satellites(abbreviated to ‘CS’) viewed from the surface of the earth is about 4.4degrees (2.2 degrees in foreign countries). To take advantage of theradio wave lens antenna to independently communicate with the respectivesatellites separated by the interval of 4.4 degrees, it is required toalign primary feeds side by side at the respective focal points near thesurface of the radio wave lens at the interval of 4.4 degrees. Furtheron this requirement, for example, if focal points of a lens antenna witha radius of 200 mm are at positions 50 mm away from the surface, thestraight line distance between the adjacent primary feeds can becalculated as 2×(200+50)×(sin(4.4/2)) to be about 19.2 mm. To meet thisrequirement, small primary feeds are needed.

Further, to use a radio wave of a same frequency, it is necessary forthe adjacent satellites separated from each other at the interval of 4.4degrees to communicate independently. To achieve this, it is requiredthat interference noises from other satellites be small. In other words,in the antenna pattern of the entire lens antenna by each primary feed,the level of a signal (sidelobe which becomes noise) from a directiondeviated by 4.4 degrees (4.4 degrees elongated direction) must be smallenough compared to the level of the signal from the main direction (mainlobe).

FIG. 14 represents an example of the antenna pattern of an antenna. Mdenotes a main lobe and signals S other than the main lobe aresidelobes.

Since, near the communication satellites, there exist not onlycommunication satellites which are 4.4 degrees away, but also many othersatellites, ITU Recommendation (ITU-R B.O. 1213), for example, providesthat it is desirable that the sidelobe levels should be lower than thatgiven by an envelope represented by the following formula (depicted by adotted line in FIG. 14).29−25 log⊖dBi(⊖: elongation[degree])

Although various methods to lower the sidelobe levels of an antenna havebeen reported, it is generally known that it can be achieved byproducing a tapered opening distribution (mainly, amplitudedistribution) of the antenna.

In order to realize this by using a lens antenna, the tapered power(amplitude) can be achieved at the radiation opening surface of the lensantenna, by having the power supplied to the center portion of the lenshigh and by gradually reducing the power while approaching the surfaceof the lens to thereby make an antenna pattern of the single primaryfeed narrow. Hereinafter, narrowing the antenna pattern is defined byusing 3 dB power width (full width at half maximum) of the antennapattern. In other words, making the antenna pattern narrow is rephrasedas being of a narrow full width at half maximum or narrowing its fullwidth at half maximum.

FIGS. 2A and 2B show the comparative antenna patterns in cases of auniform amplitude distribution and a tapered amplitude distribution. Asshown FIG. 2A, if the amplitude distribution is uniform, the levels ofthe sidelobes S compared to that of the main lobe M become relativelyhigh, whereas the sidelobes S are decreased if the amplitudedistribution is tapered as shown in FIG. 2B.

However, it is theoretically proved that, in general, the larger theopening of the antenna, the narrower the full width at half maximum, onthe other hand, the smaller the opening of the antenna, the wider thefull width at half maximum thereof. FIG. 14 represents the antennapattern of a lens antenna in the case of receiving a radio wave by aprimary feed having wide full width at half maximum, where sidelobes Sexceed the desirable envelope.

If the opening is made smaller to make the primary feed smaller, thesidelobe levels of the lens antenna become higher. On the other hand, inorder to make the full width at half maximum narrower to lower thesidelobes, the primary feed becomes larger. Therefore, making theprimary feed compact and lowering the sidelobes of the lens antenna arenot compatible with each other.

Meanwhile, a focal length of conventional parabolic antenna is greaterthan that of the lens antenna Therefore, the primary feed can bedesigned without restriction on that account and a circular horn antenna(conical horn antenna whose opening size is over 30 mm) is generallyused. However, the parabolic antenna cannot communicate with a pluralityof satellites. Further, there is a problem that the parabolic antenna isbulky, because parts such as a supporting arm or the like of the primaryfeed become bigger to accommodate the longer focal length.

It is, therefore, an object of the present invention to provide anantenna using a Luneberg radio wave lens which can keep sidelobes underthe desirable envelope level and at the same time make the size ofprimary feeds small enough to cope with satellites spaced at smallelongations. If the object is achieved, a compact and high performancemulti-beam antenna can be realized.

Further, if compact primary feeds are arranged adjacently to each other,the so-called mutual coupling phenomena occurs and the singlecharacteristic (antenna pattern) of the neighboring primary feedschanges significantly, thereby resulting in deterioration of theperformance of antennas. Therefore, it is important to reduce the effectof mutual coupling phenomena as much as possible and satisfying therequirement is also an object of the invention.

[Means to Achieve the Objects]

In order to achieve the above objects, the present invention provides aradio wave lens antenna which is constructed by combining a primary feedwith a hemispherical or spherical Luneberg radio wave lens wherein areflective plate is attached to the half-cut surface of the sphere, theprimary feed being formed of a dielectric-loaded waveguide antenna(dielectric-loaded feed) in which a dielectric body is loaded at an endopening of a waveguide. Although the waveguide constituting in theprimary feed can be tapered to have a slightly wider periphery inconsideration of the insertion of dielectric body or die-cutting inproduction, it is basically a straight tube and differs in shape fromthe waveguide used for a horn antenna.

The dielectric-loaded waveguide antenna employed in this radio wave lensantenna is preferably a rectangular waveguide loaded with a dielectricbody at an end opening (dielectric-loaded rectangular waveguide antenna)rather than a circular waveguide or a waveguide having an ellipticalcross section. The term rectangular waveguide used herein basicallyindicates a tube with a square cross section. However, it can have arectangular cross section to adjust the antenna patterns of an E-planeand an H-plane. It is also preferable that the dielectric-loadedwaveguide antenna is a choke structure antenna with an annular groovearound the front surface the waveguide.

A dielectric body loaded at the end opening of the waveguide can be of acolumn shape. The desirable shapes of the dielectric body are asfollows:

-   -   Having the dielectric body protruded from the end of a waveguide        and make the protrusion be of a taper shape having a thinned        end;    -   Making the end of the dielectric body be of a non-rotational        symmetrical shape by placing the center of the end of the        dielectric body to be at a position located off the extension of        the waveguide's center axis;    -   Removing a part of the outer periphery of the protrusion of the        dielectric body projected forward from the waveguide along the        plane of a direction intersecting the cross section of the        waveguide (cross section normal to the axis);    -   In the plane including the cross section of the protrusion,        making the dimension of the protrusion of the dielectric body        projected forward from the waveguide smaller in the disposed        direction of the primary feeds than in the direction normal to        the disposed direction of the primary feeds;    -   Making flat or round the end of the dielectric body protruded        from the waveguide by cutting out the end of the dielectric        body.

Further, the shape of the dielectric body need not be the same as thatof the waveguide. Namely, a convex lens-shaped dielectric body can beloaded at the end opening of the waveguide.

[Effects of the Invention]

In the primary feed (dielectric-loaded waveguide antenna) employed inthe radio wave lens antenna in accordance with the present invention,the effect that the power supplied to the center portion of the lens ishigh and the power is gradually reduced while approaching the surface ofthe lens is enhanced by a function of the dielectric body loaded at theend opening of the waveguide. Therefore, the full width at half maximumcan be made narrow without recourse to a large antenna opening.

Furthermore, in a rectangular waveguide, the lowest frequency (cutofffrequency) of a radio wave that can propagate through the waveguide islower compared to that of a same size circular waveguide. Thus, therectangular waveguide can ensure a desirable frequency band with asmaller tube than the circular waveguide. Therefore, the primary feedformed of a dielectric-loaded rectangular waveguide antenna can satisfya higher degree of compactness required for a primary feed combined withthe radio wave lens.

As discussed above, since the radio wave lens antenna in accordance withthe present invention is constructed by combining the primary feedincluding the dielectric-loaded waveguide antenna and the hemisphericalLuneberg radio wave lens, compactness of the primary feed can beachieved while reducing sidelobes of the lens antenna. Thus, it ispossible to realize an efficient multi-beam antenna which communicateswith a plurality of satellites spaced at small elongations.

Further, by having the dielectric body protruded from the waveguide tobe of a taper shape with a thinned end, arranging the center of the endof the dielectric body at a symmetrical position of a non-rotationalcenter, removing a part of the outer periphery of the protrusion of thedielectric body projected forward from the waveguide along the plane ofthe length direction of the waveguide and further making the dimensionof the protrusion of the dielectric body smaller in the disposeddirection of the primary feeds than in the direction normal to that, thedistance between the dielectric bodies of the adjacently disposedprimary feeds becomes large, so that the effect of suppressing mutualcoupling phenomena is enhanced.

Furthermore, by cutting out the end of the dielectric body protrudedfrom the waveguide, the length of the primary feed is shortened and,hence, the antenna can be further scaled down. Besides, excellent waterrepellence can be achieved by making the cut-out end of the dielectricbody in a round shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 offers a schematic diagram of an antenna using a hemisphericalLuneberg radio wave lens.

FIG. 2A shows an antenna pattern in case of a uniform amplitudedistribution and FIG. 2B is an antenna pattern in case of a taperedamplitude distribution.

FIG. 3A provides a perspective view for describing main parts of anexemplary primary feed and FIG. 3B illustrates a cross section of arectangular waveguide.

FIG. 4 sets forth a perspective view for describing main parts ofanother exemplary primary feed.

FIG. 5 shows a side view for describing main parts of the basicconfiguration of the primary feed.

FIG. 6 provides a side view of the main parts of the primary feedfurther having a choke structure.

FIG. 7 describes a cross sectional view of the main parts of the primaryfeed loaded with a convex lens-shaped dielectric body.

FIG. 8A depicts the disposition of two primary feeds employing circularwaveguides and FIG. 8B is the disposition of two primary feeds employingrectangular waveguides.

FIGS. 9A to 9F describe specific examples for the cross sectional shapeof the protrusion of the dielectric body.

FIGS. 10A to 10D provide specific examples for the side shape of theprotrusion of the dielectric body.

FIG. 11 shows an example of suppressing the coupling by using primaryfeeds loaded with dielectric bodies of a shape having a non-rotationalsymmetric end.

FIGS. 12A and 12B show an example for suppressing the coupling bycutting out a part of the dielectric body protruded from the waveguide.

FIG. 13 presents antenna patterns for comparing weak coupling withstrong coupling.

FIG. 14 shows an antenna pattern of an antenna with wide full width athalf maximum.

FIG. 15 describes an antenna pattern of an antenna in case of using adielectric-loaded waveguide antenna as a primary feed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 3A to 13 represent preferred embodiments of the present invention.The basic structure of a radio wave lens antenna in accordance with thepresent invention is identical to that shown in FIG. 1 (there can be theone that employs a spherical Luneberg radio wave lens without areflective plate) except a primary feed and a method for disposing twoprimary feeds closely. Thus, only the structures or the dispositionmethods of the primary feeds are described in the embodiments.

A primary feed 3 in FIG. 3A is constructed by loading a dielectric body6 having a polygonal column shape at the end opening of a rectangularwaveguide 4.

On the other hand, a primary feed 3 in FIG. 4 is constructed by loadinga dielectric body 6 of a circular column at the end opening of acircular waveguide 5 (it can be an elliptical waveguide).

A rectangular waveguide, in particular, a waveguide with a square crosssection, offers better space efficiency and the best compactness of aprimary feed. Nevertheless, depending on the performance of the loadeddielectric body, the primary feed 3 can be scaled down to a desired sizeby using a circular or an elliptical waveguide.

The material of the waveguides 4 and 5 can be a metal such as brass oraluminum or a die-casting with a high production yield. For the size ofthe waveguides 4 and 5, each side can be not greater than 18 mm (both aand b in FIG. 3A are not greater than 18 mm) in case of a rectangularwaveguide for 12 GHz frequency band, for example. Therefore, even thoughthe interval between primary feeds is 19.2 mm as described above, theprimary feeds can be arranged at desired positions without interferingeach other.

Further, the dielectric body 6 is preferably made of material of arelatively low dielectric constant and a small dielectric loss (tanδ),such as polyethylene.

The length of the dielectric body 6 (L in FIG. 5) is determined based onthe full width at half maximum of the primary feed 3.

FIG. 6 represents a primary feed 3 which has a choke structure by makingan annular groove 7 around the front surface of a waveguide 4. By usingthe choke structure as well, sidelobes of an individual primary feed canbe effectively reduced and, sidelobe levels are also lowered. This chokestructure is also useful in a primary feed employing waveguides otherthan the rectangular waveguide.

The shape of the dielectric body 6 loaded to the waveguide is notlimited to the column shape. FIG. 7 depicts a convex lens-shapeddielectric body 6 loaded at the end opening of a rectangular waveguide 4(or a circular waveguide 5). The dielectric body 6 of such shape can bealso used.

FIGS. 8A to 13 provide useful primary feeds when intervals betweenelements are small and there is a potential coupling problem.

In FIGS. 8A and 8B, there are respectively shown two primary feeds 3using circular waveguides 5 and using rectangular waveguides 4 which arearranged at the interval of P corresponding to the distance betweengeostationary satellites. The rectangular waveguide is advantageous inthat it has a smaller tube size than the circular waveguide when adaptedto a radio wave of a same frequency. Therefore, in case two primaryfeeds 3 are arranged at the interval of P by using the rectangularwaveguides 4, the interval P1 between dielectric bodies 6 of bothprimary feeds is larger than the case by using the circular waveguides 5and, thus, the coupling becomes weaker.

Each primary feed is arranged toward the center of the radio wave lensand thus the interval between the adjacent primary feeds becomesnarrower when approaching closer to the ends of the elements. Therefore,it is preferable that the dielectric body 6 protruded from the waveguideis of a taper shape having a thinned end. FIGS. 9A to 9F illustrateexemplary cross sectional views of the protrusions. In all theexemplified protrusions, the width w (minor axis of an ellipse) issmaller than the dimension d in the direction normal to the width (majoraxis of an ellipse). Thus, by setting the direction of the dielectricbody 6 in such a manner that the width direction coincides with thearranged direction of the primary feeds, a distance between thedielectric bodies of the adjacent primary feeds can be made larger.

FIG. 10 shows examples in which each of the protrusions of thedielectric bodies 6 from the waveguides has a taper shape having athinned end. In FIG. 10A, the dielectric body 6 protruded from thewaveguide is of an elliptical or polygonal cone shape while the apex ofthe cone is located at the center axis of the base of the cone. Bycutting out the end of the protrusion as shown in FIG. 10B or 10C, thedimension of the primary feed along the axial direction is reduced.Thus, since the distance from the surface of the radio wave lens to thefocal point becomes small, the size of the antenna can be further scaleddown.

Further, considering water repellence in case of being wetted by rain,it is preferable that the cut-out end of the dielectric body 6 is of around shape as shown in FIG. 10C rather than flat as shown in FIG. 10B.

When the protrusion of the dielectric body 6 is of a cone-shape, thevertex is located off the center axis of the base of the cone asillustrated FIG. 10D. In the present invention, two primary feeds 3 eachhaving the dielectric body 6 whose protrusion is of a non-rotationalsymmetrical shape as described above are disposed closely. If twoprimary feeds are disposed closely, mutual coupling phenomena occurs,resulting in the distortion of radio waves captured by the respectiveprimary feeds. However, the distortion can be reduced by disposing theends of the protrusions of the dielectric bodies 6 at off-centeredpositions in such manner that they are remotely spaced apart from eachother as shown in FIG. 11.

As illustrated in FIGS. 12A and 12B, a part of the outer periphery ofthe protrusion of the dielectric body 6 is cut out along the plane of adirection intersecting the cross section normal to the axis of thewaveguide and such dielectric bodies 6 are loaded to the waveguides ofthe adjacent primary feeds in such a manner that the cut out surfaces ofthe outer peripheries face each other. The coupling can be also reducedin such a structure. Although the cut out surface of the outer peripheryof the dielectric body 6 is shown to be perpendicular to the crosssection normal to the axis, it need not be.

In FIG. 13, the solid line and the dashed dotted line show antennapatterns with weak coupling and strong coupling, respectively. If thecoupling is limited by using a rectangular waveguide and by tailoringthe shape of a dielectric body, the distortion of a radio wave can bereduced and, therefore, communication sensitivity for the geostationarysatellites can be improved.

Further, by combining the base portion of the waveguide where thedielectric body is loaded with a circuit board and mounting a low noiseamplifier (LNA), a frequency conversion unit (converter) and the like onthe circuit board, the primary feed 3 can be advantageously constructedas a low noise block down (LNB) for a satellite broadcasting antenna.

All of the above described primary feeds satisfy the following basicproperties 1)–4) which are required in the element for the radio wavelens antenna of FIG. 1. Consequently, the requirement of the lowsidelobe can be satisfied, which makes independent communications withadjacent satellites possible and which is a collective characteristicwith a Luneberg radio wave lens:

-   -   1) The size is equal to or less than 0.8λ (λ: wavelength, for        example, about 25 mm in case of 12.5 GHz frequency);    -   2) For example, the full width at half maximum of about 50        degrees can be realized;    -   3) It is a linearly polarized wave antenna for common use for        both vertical (V) and horizontal (H) linearly polarized waves        (if this condition is satisfied, it can be applied to the        circularly polarized wave antenna); and    -   4) The antenna patterns of the E-plane and H-plane (see FIG. 3B)        can be identical as much as possible.

FIG. 15 illustrates the effect of lowering the sidelobes in the antennapattern of the lens antenna when the aforementioned dielectric-loadedwaveguide antenna (which uses a rectangular waveguide) is employed as aprimary feed 3 of the radio wave lens antenna in FIG. 1.

As shown, if a dielectric-loaded waveguide antenna featuring the presentinvention is used, the sidelobes S become smaller than the desiredenvelope (dotted line in the drawing) and, therefore, it is possible toindependently communicate with the satellites spaced at smallelongations (for example, an interval of 4.4 degrees).

Simultaneously, scaling down of the primary feed is achieved and spatialinstallation restriction of the primary feed is relaxed; and, thus, itis possible to communicate with a plurality of satellites.

1. A radio wave lens antenna comprising: a hemispherical radio wave lensfor focusing radio wave beams; a reflective plate attached to a half-cutsurface of the sphere of the radio wave lens for reflecting radio wavesincoming from the sky or radiated toward targets; and primary feedspositioned at arbitrary radio wave focus points of the radio wave lensfor transmitting or receiving the radio waves, wherein the primary feedsinclude at least one pair of primary feeds installed closely and each ofthe two closely disposed primary feeds includes a dielectric loadedwaveguide antenna where a dielectric body is loaded at an end opening ofa waveguide, a center of the end of the dielectric body being locatedoff the extension of the waveguide's center axis and the centers of theends of the dielectric bodies of the two closely disposed primary feedsbeing disposed at off-centered positions such that the centers areremotely spaced apart from each other.
 2. The radio wave lens antenna ofclaim 1, wherein the dielectric-loaded waveguide antenna is adielectric-loaded rectangular waveguide antenna where the dielectricbody is loaded at the end opening of a rectangular waveguide.
 3. Theradio wave lens antenna of claim 1, wherein the dielectric body of thedielectric-loaded waveguide antenna is protruded forward from thewaveguide and a protruded portion of the dielectric body is of a tapershape having a thinned end.
 4. The radio wave lens antenna of claim 3,wherein an end of the dielectric body protruded from the waveguide iscut out such that the end of the dielectric body is of flat or a roundshape.
 5. The radio wave lens antenna of claim 3, wherein in a planeincluding a cross section of the protruded portion of the dielectricbody protruded forward from the waveguide, a dimension of the protrudedportion in a disposed direction of the two primary feeds is smaller thanthat in a direction normal to the disposed direction of the two primaryfeeds, the cross section of the protruded portion being normal to thewaveguide's center axis.
 6. The radio wave lens antenna of claim 5,wherein an end of the dielectric body protruded from the waveguide iscut out such that the end of the dielectric body is of flat or a roundshape.
 7. The radio wave lens antenna of claim 1, wherein the dielectricbody is protruded forward from the waveguide and a part of an outerperiphery of a protruded portion of the dielectric body is removed alonga plane of a direction intersecting a cross section of the waveguidenormal to the center axis thereof.
 8. The radio wave lens antenna ofclaim 7, wherein in a plane including a cross section of the protrudedportion of the dielectric body protruded forward from the waveguide, adimension of the protruded portion in a disposed direction of the twoprimary feeds is smaller than that in a direction normal to the disposeddirection of the two primary feeds, the cross section of the protrudedportion being normal to the waveguide's center axis.
 9. The radio wavelens antenna of claim 8, wherein an end of the dielectric body protrudedfrom the waveguide is cut out such that the end of the dielectric bodyis of flat or a round shape.
 10. The radio wave lens antenna of claim 7,wherein an end of the dielectric body protruded from the waveguide iscut out such that the end of the dielectric body is of flat or a roundshape.
 11. A radio wave lens antenna comprising: a spherical radio wavelens for focusing radio wave beams; and primary feeds positioned atarbitrary radio wave focus points of the radio wave lens fortransmitting or receiving the radio waves, wherein the primary feedsinclude at least one pair of primary feeds installed closely and each ofthe two closely disposed primary feeds includes a dielectric loadedwaveguide antenna where a dielectric body is loaded at an end opening ofa waveguide, a center of the end of the dielectric body being locatedoff the extension of the waveguide's center axis and the centers of theends of the dielectric bodies of the two closely disposed primary feedsbeing disposed at off-centered positions such that the centers areremotely spaced apart from each other.
 12. The radio wave lens antennaof claim 11, wherein the dielectric-loaded waveguide antenna is adielectric-loaded rectangular waveguide antenna where the dielectricbody is loaded at the end opening of a rectangular waveguide.
 13. Theradio wave lens antenna of claim 11, wherein the dielectric body of thedielectric-loaded waveguide antenna is protruded forward from thewaveguide and a protruded portion of the dielectric body is of a tapershape having a thinned end.
 14. The radio wave lens antenna of claim 13,wherein an end of the dielectric body protruded from the waveguide iscut out such that the end of the dielectric body is of flat or a roundshape.
 15. The radio wave lens antenna of claim 13, wherein in a planeincluding a cross section of the protruded portion of the dielectricbody protruded forward from the waveguide, a dimension of the protrudedportion in a disposed direction of the two primary feeds is smaller thanthat in a direction normal to the disposed direction of the two primaryfeeds, the cross section of the protruded portion being normal to thewaveguide's center axis.
 16. The radio wave lens antenna of claim 15,wherein an end of the dielectric body protruded from the waveguide iscut out such that the end of the dielectric body is of flat or a roundshape.
 17. The radio wave lens antenna of claim 11, wherein thedielectric body is protruded forward from the waveguide and a part of anouter periphery of a protruded portion of the dielectric body is removedalong a plane of a direction intersecting a cross section of thewaveguide normal to the center axis thereof.
 18. The radio wave lensantenna of claim 17, wherein in a plane including a cross section of theprotruded portion of the dielectric body protruded forward from thewaveguide, a dimension of the protruded portion in a disposed directionof the two primary feeds is smaller than that in a direction normal tothe disposed direction of the two primary feeds, the cross section ofthe protruded portion being normal to the waveguide's center axis. 19.The radio wave lens antenna of claim 18, wherein an end of thedielectric body protruded from the waveguide is cut out such that theend of the dielectric body is of flat or a round shape.
 20. The radiowave lens antenna of claim 17, wherein an end of the dielectric bodyprotruded from the waveguide is cut out such that the end of thedielectric body is of flat or a round shape.